Today, there’s an outcry to lower speed limits to combat pedestrian fatalities. Wouldn’t it be great if just putting up signs worked? But it probably won’t.

I agree that New York City, not the state, should dictate local speed limits, but I have found no evidence that a blanket change in the city limit from 30 mph to 25 mph or even 20 mph would work.

You may say there’s no harm in just slowing all cars down. But some studies, mostly on highways, have found that this can actually increase crashes. Some drivers lower their speeds; others keep driving as they did. The speed differential between cars increases, and that increases crash potential.

Most readers are probably going to come away from the piece with the notion that 20 mph speed limits are misguided, which is too bad, because Sam’s actual proposals are good (though not sufficient to bring traffic deaths down to a level approaching zero).

The campaign for blanket 20 mph speed limits is about much more than putting up signs. For one thing, it’s getting the word out that speed matters.

Right now, most people don’t even know what the speed limit is on NYC streets[2]. They don’t get why the decision to drive 35 or even 40 mph is an unnecessary risk that, applied to millions of trips every day, results in far more injuries and deaths than if we all stuck to 20 or 25 mph. The campaign for 20 mph can change that. It’s getting a ton of coverage and a lot of attention from elected officials right now. NYC has a window of opportunity to broadly communicate why driving faster than 20 mph impedes reaction times, leading to more crashes, and drastically increases the severity of injuries in the event of a crash.

As for the specific claims about blanket 20 mph speed limits, the speed differential argument that Sam makes may apply to highway conditions, but urban streets are a different beast. In the UK, blanket “signs-only” 20 mph zones are an increasingly popular low-cost first step to improve safety[3]. Research on signs-only slow zones may be scant, but the evidence so far suggests there are real safety benefits, and no studies have shown the type of downside that Sam predicts. Danny Dorling, a professor of geography at Oxford, cites research from Scotland [PDF[4]] finding that “20 mph (32 kph) limits without traffic calming measures at 78 sites found reductions in speed and casualties, concluding that such limits offer a low cost option for promoting road safety.”

The broader point is that a citywide 20 mph speed limit, while not sufficient to achieve drastic traffic fatality reductions on its own, would be a huge step toward making safe driving speeds the social norm. It would reset expectations and raise the bar for engineering and policing. If New Yorkers start thinking of law-abiding driving as adhering to a 20 mph maximum speed, it will be that much clearer that streets need better design and enforcement. Vision Zero is a huge undertaking, and it’s hard to see how it can be accomplished without a significant across-the-board reduction in vehicle speeds on all streets.

I know this wasn’t Gridlock Sam’s intent, but his column is going to muddy what should be a clear message: Speed kills, even speeds most people currently consider acceptable.

Article printed from
Streetsblog New York City:
http://www.streetsblog.org